This invention relates to hydraulic clutch actuators and more particularly to hydraulic clutch actuators employing a damper mechanism.
Hydraulic actuators are known for operating a mechanism at a remote location by way of a master cylinder connected to a slave cylinder installed at the remote location. A conduit interconnects the master cylinder to the slave cylinder and the hydraulic apparatus is filled with hydraulic fluid such that, when the piston of the master cylinder is actuated, the piston of the slave cylinder and consequently the piston rod or output member is simultaneously actuated by displacement of the hydraulic fluid from the master cylinder to the slave cylinder through the conduit.
More particularly, it is known to provide such a hydraulic actuator for operating the clutch of a motor vehicle so that, when the clutch pedal of the vehicle is depressed by the driver, the slave cylinder is actuated to operate the clutch in known manner. Preferably, as described in U.S. Pat. No. 4,599,860 assigned to the assignee of the present application, the clutch actuator is provided to the motor vehicle manufacturer in an assembled pre-filled form to simplify installation of the actuator on the vehicle, avoid the inconvenience of potential spillage of hydraulic fluid during on-line filling, eliminate the necessity to bleed or purge the lines of the actuator to facilitate the filling process, and eliminate the need to test the actuator after installation and filling. Whereas hydraulic clutch actuators, and particularly pre-filled clutch actuators, have enjoyed significant commercial success, they have the ability to transmit vibrations backwardly through the system from the clutch to the clutch pedal with the result that the operator may experience unpleasant vibrations at the clutch pedal.
Specifically, imbalances in the crank shaft of the vehicle engine or engine firing impulses are transmitted to the flywheel which undergoes a swashing movement, the flywheel swashing movement in turn leads to vibrations of the spring fingers of the clutch release mechanism, the vibrations of the spring fingers are transferred to the release bearing of the clutch, and the vibrations propagate backwardly through the hydraulic fluid in the slave cylinder, through the hydraulic fluid in the conduit interconnecting the slave cylinder and the master cylinder, through the hydraulic fluid in the master cylinder, and then through the master cylinder pushrod to the clutch pedal where they are experienced by the operator as vibrations of the clutch pedal. The propagated vibrations also generate a pedal growl which is audible to the operator as well as a clutch roar which may also be audible to the operator.
Various devices have been proposed in an attempt to attenuate these vibrations, for example, tuned masses have been attached to various parts of the clutch system including the clutch release lever, the slave cylinder pushrod, and the clutch pedal. Rubber dampers have also been employed in the master cylinder pushrod, rubber hose sections have been employed in the conduit interconnecting the master cylinder and the slave cylinder, and various damper devices have been proposed for installation in the interconnecting conduit. In particular, a damper device as shown in British Patent Specification 1,562,709 or as shown in U.S. Pat. Nos. 4,998,609 or 5,320,203, all assigned to the assignee of the present invention, may be installed in the conduit interconnecting the master cylinder and the slave cylinder.
Whereas these prior art devices have been successful in varying degrees in attenuating the vibrations in the system, they are dedicated to attenuating vibrations in a predetermined frequency range and accordingly are ineffective in attenuating vibrations falling outside of the predetermined range. Specifically, damping devices that are effective in attenuating the high frequency vibrations occurring in the system during engagement and disengagement of the clutch during normal driving are generally ineffective in attenuating the low frequency vibrations appearing at the clutch pedal during engine idle conditions with the transmission in neutral.
This invention is directed to the provision of an improved damper device for use in association with a hydraulic clutch actuator.
More particularly, this invention is directed to the provision of an improved damper device for use in association with a hydraulic clutch actuator which effectively attenuates both high frequency and low frequency vibrations in the system.
This invention relates to a damper for provision in a hydraulic actuator system between a master cylinder and a slave cylinder of the system. The damper includes a housing including port means for connection in the system and defining a chamber in communication with the port means, and diaphragm means carried by the housing and extending across the chamber so as to form a boundary wall of the system so that the diaphragm means may deflect in response to vibrations transmitted through the hydraulic fluid in the system to effect damping of the vibrations.
According to the invention, the damping means is a compound structure including an elastomeric diaphragm extending across the chamber with one face thereof communicating with the port means so as to form the system boundary wall so that the elastomeric diaphragm may deflect in response to low frequency vibrations transmitted through hydraulic fluid in the system to effect damping of the low frequency vibrations, and a further diaphragm positioned parallel to and proximate the other face of the elastomeric diaphragm so as to form a backup for the elastomeric diaphragm so that the elastomeric diaphragm may deform against the further diaphragm in response to high frequency vibrations transmitted through the hydraulic fluid to cause deflection of the further diaphragm to effect damping of the high frequency vibrations. This arrangement allows the damper to effectively attenuate both low frequency and high frequency vibrations encountered in the associated hydraulic system.
According to a further feature of the invention, the elastomeric diaphragm is a rubber diaphragm and the further diaphragm is a spring steel diaphragm. This particular combination of diaphragm materials allows the elastomeric diaphragm to deform elastically against and into conformity with the spring steel diaphragm whereafter the spring steel diaphragm may deflect to absorb high frequency vibrations.
In one embodiment of the invention, the spring steel diaphragm has a dished configuration including a peripheral portion engaging a peripheral portion of the confronting face of the elastomeric diaphragm and a central recessed portion positioned proximate but spaced from a central portion of the other face of the elastomeric diaphragm. With this arrangement the elastomeric diaphragm may deform downwardly elastically into conformity with the recessed portion of the stainless steel diaphragm whereafter the stainless steel diaphragm may deflect to absorb high frequency vibrations.
In a further embodiment of the invention, the elastomeric diaphragm includes a generally planar main body portion positioned against one face of the stainless steel diaphragm and a plurality of spaced bubble portions upstanding from the main body portion of the elastomeric diaphragm and defining void areas therebeneath between the elastomeric diaphragm and the stainless steel diaphragm. With this arrangement the bubbles may elastically flatten to absorb low frequency vibrations whereafter, following flattening of the bubbles against the underlying stainless steel diaphragm, the stainless steel diaphragm may deflect to absorb high frequency vibrations.
The invention also contemplates a method of damping vibrations in a hydraulic actuator system of the type including a master cylinder and a slave cylinder. According to the invention methodology, an elastomeric diaphragm is positioned in the system between the master cylinder and the slave cylinder with one face of the elastomeric diaphragm in fluid communication with hydraulic fluid in the system, whereby the elastomeric diaphragm may deflect in response to low frequency vibrations transmitted through the hydraulic fluid in the system to effect damping of the low frequency vibrations, and a further diaphragm is positioned in the system generally parallel to and proximate the other face of the elastomeric diaphragm so as to form a backup for the elastomeric diaphragm so that the elastomeric diaphragm may deform against the further diaphragm in response to high frequency vibrations transmitted through the hydraulic fluid to cause deflection of the further diaphragm to effect damping of the high frequency vibrations. This methodology allows the damper to act to effectively dampen both low frequency and high frequency vibrations occurring in the hydraulic system.
Other objects, advantages and applications of the present invention will become apparent to those skilled in the art when the following description of the best modes contemplated for practicing the invention are read in conjunction with the accompanying drawings.